Will missing vapor barrier & unvented crawlspace make Radon levels elevated ?

I tested a brand new home the other day & the Radon level was at 19.3 . There was no vapor barrier in the 3’ tall crawlspace & no vents in the crawlspace walls. Would these missing items contribute to elevated Radon levels ? Could a person possibly eliminate enough radon this way to avoid the high remediation cost ? I have a test to do tommorrow whose contractor friend believes all of the above is possible. The house tommorrow has no vapor barrier on the crawlspace either dirt & no vents.


Its all about airsealing. Makes sense to me.

Moisture alone would justify a vapor barrier in the crawl. But logically it might lower the radon level if it was well done. But no way to be sure until you try it.

Exactly… Putting a vapor barrier in and venting the space will logically reduce the radon levels, but there is really no way to know how much unless you try and re-test. It’s very possible that a mitigation system will be required anyway.

If this helps;

Mitigation in Existing Homes

The process in which radon entry is controlled is referred to as mitigation. Radon can effectively be managed and reduced in homes have elevated methods. These methods differ according to the building type.

Active Soil Depressurization (ASD) is the most common mitigation type and is proven to be very effective on slab and basement homes. Sub-membrane Depressurization is most often used in crawlspaces.

Active Soil Depressurization is a simple process. In the lowest level of the home, a hole is cored in the concrete slab (typically in a corner or near the foundation wall) and soil and/or stone is removed through the cored hole. Piping and a small fan are installed to reroute the radon to the exterior of the house.
The piping and fan are usually routed and installed in the garage (if no living area above) or on the exterior of the house. Most systems can be installed from $1100 - $1600. *Some houses do require multiple cores and / or fans to adequately reduce the Radon level which does involve a greater cost. *

Sub-membrane Depressurization is used in crawlspaces to control soil gasses (Radon & moisture). A vapor barrier is added or improved above the ground in the crawlspace. Piping and a small fan are used to reroute the radon laden gas from underneath this vapor barrier to an outside vent on the top of your house. This type of system has recently been proven effective in reducing and controlling moisture levels in crawlspaces that can contribute to indoor air quality and mold problems. The cost of these systems is dependant of individual conditions of the space.


The crawl space vents would have to be closed when you are doing the radon testing. As for the Vapor Barrier the radon gas will still go through it. This is a very confusing subject but we have to remember everything is made of molecules and the gas will slip through the molecules of the plastic also.
The vents and vapor barrier need to be installed to keep the relative humidity down and prevent mold growth.

I’d imagine that a vapor barrier and vents will lower radon levels, but the radon gases will still seep out from under the poly.

It’s really quite simple.

Test the Radon levels and if it’s higher than 4.0…mitigate. I wouldn’t play games with cheaper mitigation methods. The 1200 dollar fee to install a proper mitigation system is not expensive if it’s saving lives.

I think you received your answer and I apologise up front, but if you do not understand this concept, what are you doing testing for Radon?

I would extrapolate, but I am in a certification class as we speak, something I recommend you should seriously consider before offering this service.

Mr. Anderson, I knew the answer ahead of time, I was getting a variety of opinions, & I would appreciate in the future if would only reply to my posts with an appropriate answer & not question my qualifications. You set a great example for the new people showing your integrity with such a reply.

In short, the answer is yes it can. But, is that the only solution? As someone else said in a post by discussing ASD probably not. Without the proper system in place and ventilation in the crawl space radon can be sucked up into the main living area of a structure. I’m not sure what your client was looking for in your inspection and what kind of background information you received, but I’d make sure to have them find a qualified mitigation contractor to further the necessary repairs or systems to resolve the problem. Go back and check it when they’re done for a post-verification examination. Go from there.

The first home I recomended they consult a qualified remediator & gave them a list of them in the area, The latter home mentioned is the one the current occupants want tested again. The tested it themselves & it was 15.0. The occupants contacted a friend who’s a general contractor who’s not qualified to install remediation equipment & claims to have been doing it for years, & want him to do the remediation when my test is done, this is the first I’ve heard of him doing this kind of work. It sounds like someone going into business building houses just because they own a hammer & a saw, ya know what I mean?. I have recommend they only use qualified mitigators who are in the business, not a handyman/do-it-all just because he’s probably cheaper, I will also supply them with the list of mitigators I have also, thanx for the replies guys…

I have nad many clients who try to fix something, on the cheap. Do their own Radon or mold remediation or hire a “handyman” to replace their old electric panel or a “couple of Mexican guys” to install a new roof.

I try to disuade them from this, but people will be people.

Many times, I get a call back, asking me to check on the crappy job that was done so they could sue the sub-standard worker. I, clearly, explain, “You got the job you paid for, and I will testify in court to that. Are you sure you want me to do that?”

Hope this helps;

Thanx Will, the reason this bothers me so is that the gal that’s heading up this deal is trying to get into contracting & some of the clowns she’s using as her subs are the ones I’m worried will get her in trouble by using these “Oh yea, I’ve done several of these & all seem to be fine” attitudes & her being stubborn & niave enough to believe them. I have to just do my job as I’ve been trained, make my recommendations (which will not be for the homeowner to her guys) & hope I don’t step on any landmines in the process, ya know how it goes…

I would appreciate that you ask your damn questions appropriately.

Seeing you knew the answer to the forthcoming, why the hell did you ask it?

If you asked an appropriate question, I would have answered it appropriately.

Seeing you know the difference: shame on you!

Seeing you are a member: you can kiss *****

You ask, you get a reply. I was ******* nice and apologised before I posted the "(now I know) your a ******* idiot!

I am not being a hard ***!
I spent several thousand dollars in a certification class (4 DAYS) where your stupid *** question was simply “stupid ***”.

If you can’t take a simple : go get some training!

Get off this board, and get some training!

I lost two jobs today from HI’s that do IT at $230 @ 3K SF!


I did EPA Radon 10 years ago and I likely forgot more than you now!
If you want to match wits, have at it!
But you, my friend have no clue!

I’m willing to teach you a thing or two. But at this point, you can do it on your own!


David, be Happy:):):):):):):D:D:D:D:D

Hey Marcel, did you get any on ya ? Ya better duck, My, My, My, what a spew… Haven’t seen that many asteriks used in a long time,

Now, now, Brother NACHI members. I don’t know the whole history, here, and I don;t want to. But, some things have to be said.

Mustn’t feed on each other.

  1. If one is qualified (as in special training to do a particular type of inspection) then do it. If one is skirting the lack of state law, then one is not qualified and is in a load of trouble (to themselves, eventually) and to NACHI.

  2. This also applies to various subs and contractors and simple “handumen”. If one is not qualified (if there is a state requirement, meet it. If there is not, meet the current federal requirements. Just that simple.), then DO NOT do it. I don’t care is you can “make the money”. Why would you want to screw your clients that way.

  3. Many subs and contractors and handymen (and Realtors) take advantage of this. Their thinking (or lack thereof) is:

  • If it is not, specifically, prohibited, it is OK.
  • If it is prohibited, but they do not enforce, or can’t catch me, it is OK.
  • If I can get away with it, and get paid, it is OK.


And why would ANY real professional want to be associated with these type of people?

I will not lie, cheat or steal, nor will I tolerate those who do.

Simple, clean and easy.

You want to play the same unethical game as some of the scum bag builders we are always complaining about, that is your problem.

But, I would posit that you are not professional, ethical or moral.

And, by being a member of NACHI, you bring us all down.

Again, I am NOT casting any aspersions on anyone. I don’t know the details. But, if you are doing this, get the heck off my Associations’s board. We don’t need, want nor will we tolerate you kind.

Nuff said.

Thanks Will

Marcel :):smiley:

No not nuff said, I have been on this board & a quiet member of NACHI longer than any of you that have replied with these childish attacks, hope you are proud of yourself, bet it makes it hard for you to walk don’t it. I shouldn’t have to explain the post again so you can understand the simple situation I was seeking opinions on. A professional opinion or advice, isn’t that what most people are looking when they view this board & not for people making fools out of ourselves. They can find those boards anywhere & not have to pay to do it. I know there are those watching & considering NACHI & wondering, “Wow, all they do is argue & belittle people on like the other places do, it show thr true colors of these guys & I’m not sure I want to be a part of an association like that” Hum, The attacks (Get off MY board) are uncalled for & shows the inability to deal rationally with someone rather than get mad & shows the lack of professionalism & integrity of those who do so. It’s actually appalling & the moderators shouldn’t allow it, if you want to yell & scream & throw a name-calling tantrum, then go to the the “Not for everyone” forum & slug it out, or Face Book. THAT my friend is what hurts NACHI’S integrity. It makes those doing it look like a bunch of arrogant know-it-alls & cyber bullies who probably wouldn’t talk to someone like that face to face. Normal people just want an answer to their question. And please before someone comes back with another name calling reply, take a deep breath, & ponder this post & you will see the truth in it. Unbelievable that I have to even reply to something like this.